以磁域為基礎之磁電耦合效應所建構之奈/微米級電磁鐵

Abstract

本論文提出以條紋(複數)磁域為基礎之磁電耦合效應所建構之奈/微米級電磁鐵。此奈/微米級電磁鐵主要是由鎳長方形奈/微米結構及具有上下電極之異向性壓電性質之鈮鎂酸鉛塊材所組成，設計概念為:(I)以透過減少條紋磁域數目使出平面方向之磁域強度在磁場輔助之下產生更劇烈變化，(II)搭配異向性壓電特性(亦即，施加電場會使壓電材料之X軸與Y軸方向產生不同量值之應變)之鈮鎂酸鉛塊材，(III)結合逆磁電效應所產生之易磁化軸(easy axis)轉換特性。根據上述這些設計, 施加電場驅動此奈/微米級電磁鐵時，會使電磁鐵之磁域之磁化方向產生劇烈變化，並更進一步地利用幾何不連續處之磁域不穩定特性來使此電磁鐵在外加電場驅動下會在幾何不連續處產生更激烈的磁域變化。據此, 便可達成以電場驅動並控制奈/微米級電磁鐵之磁化方向之目的。 據上述設計，透過製程參數優化，我們成功地製造出奈/微米級電磁鐵，並透過各式材料性質檢測方法證實所製造之電磁鐵是具備了我們所預定之特殊性質。最後, 電磁鐵之性能測試結果則證實了，在輔助磁場所產生之磁域變化後, 可用電場控制之方式使條紋磁域產生平面上之磁化方向旋轉，同時使出平面方向磁域強度產生變化，更在幾何不連續處會產生特異之變化, 這些結果乃是奈/微米級電磁鐵未來發展之關鍵技術。

In this thesis, I proposed a novel stripe-domain (multi-domain) based magnetoelectric-coupled micro/nanoscale electromagnets. The micro/nanoscale electromagnets consist of micro/nanoscale multi-domain Ni rectangular-structures deposited on the top electrode of an anisotropic piezoelectric PMN-PT bulk. The design concept includes: (I) The domain’s intensity/magnitude along out-of-plane direction under a magnetic field is increased when the number of magnetic domains is decreased. (II) Using PMN-PT bulk with anisotropic piezoelectric property enables that X-axial and Y-axial strain with different magnitude are generated after the electric field is applied to PMN-PT). (III) Easy-axis exchange driven by the converse magnetoelectric effect. According to these concepts, when the electric field is applied to the PMN-PT, the magnetization-direction of the domains of the Ni micro/nano-structures is significantly. Furthermore, because magnetic domains are significantly influenced by geometric discontinuities of the Ni micro-nanostructure, we can observe special domain-transformation on the geometrical discontinuities by the above-mentioned approach (i.e., applying electric field, etc.,). Due to these, using the electric field to control the magnetization-direction of the micro/nano electromagnets is achieved. According to the design, the micro/nanoscale electromagnets were accordingly and successfully fabricated by an optimized MEMS/NEMS fabrication-process. After fabrication, we characterized the specific material properties utilized by the electromagnets. The characterization results show that the fabricated electromagnets exhibit the expected decent functions. Finally, we tested the performance of the electromagnets. The test results show that after the magnetization-direction of the magnetic domain is pre-changed by an external magnetic field, the multi/stripe-domains’ magnetization-direction is rotated along the in-plane direction and the intensity of the domain is changed along the out-of-plane direction by the applied electric fields. Moreover, the domains have special domain-transformation on the geometrical discontinuities of the Ni micro/nano-structures. These experimental results are important milestones for developing future electromagnetic MEMS/NEMS.